1. Field of the Invention
This invention relates generally to sensor devices for detection of electromagnetic emissions from an indicator having an analyte of interest permeating therethrough, wherein the characteristics of the emissions vary as a function of the concentration of the analyte. More particularly, the invention relates to improvements in the design and performance of such sensor devices.
2. Background Art
U.S. Pat. No. 5,517,313, the disclosure of which is incorporated herein by reference, describes a fluorescence sensing device comprising a layered array of a fluorescent indicator molecule-containing matrix (hereafter “fluorescent matrix”), a high-pass filter and a photodetector. In this device, a light source, preferably a light-emitting diode (“LED”), is located at least partially within the indicator material, such that incident light from the light source causes the indicator molecules to fluoresce. The high-pass filter allows emitted light from the indicator molecules to reach the photodetector, while filtering out scattered incident light from the light source. An analyte is allowed to permeate the fluorescent matrix, changing the fluorescent properties of the indicator material in proportion to the amount of analyte present. The fluorescent emission is then detected and measured by the photodetector, thus providing a measure of the amount or concentration of analyte present within the environment of interest.
One advantageous application of a sensor device of the type disclosed in the '313 patent is to implant the device in the body, either subcutaneously or intravenously or otherwise, to allow instantaneous measurements of analytes to be taken at any desired time. For example, it is desirable to measure the concentration of oxygen in the blood of patients under anesthesia, or of glucose in the blood of diabetic patients.
Since the invention of the device described in the '313 patent, the present inventors have developed a number of design improvements which have significantly enhanced the performance, reliability and longevity of optical sensor devices of the type described in the '313 patent.
In particular, because of the size and weight restrictions placed on such sensor devices especially for in-vivo or in-situ applications, it is important to maximize the efficiency of the available indicator matrix in order to obtain a more reliable and accurate measurement signal, while minimizing power consumption and heat generation. Additionally, the sensor device design should permit cost-effective high volume manufacturing at a reasonable selling price. Further, maximizing the longevity of the device is desirable especially where the device must be implanted in the body for in-situ detection of bioanalytes.